It is well established in the art to produce ophthalmic lenses, more specifically hard and soft contact lenses, in an automated production process with reusable molds. In mass production of contact lenses, specifically so-called disposable lenses, a large number of contact lenses must be manufactured in a relatively short period of time. In an advantageous method of mass production, a lens forming material, e.g., a polymer or prepolymer solution, such as a polymer or prepolymer solution containing water, is introduced into a female mold half, the casting mold is closed by the respective male mold half and then the lens forming material is polymerized and/or cross-linked with ultraviolet (UV) light. The mold halves mask the UV light in the respective areas, which are outside of the areas required for contact lens production. Such mass production of contact lenses may be performed in a closed loop process and is described in WO 98/42497, for example. Suitable polymers formed by photochemical polymerization of suitable prepolymers include polymers based on polyvinyl alcohols (PVA) or silicone hydrogels (SiHy) as well as based on polyethylene glycols (PEG).
There are known lens forming materials which include a solvent, for example silicone hydrogels (SiHy), which may contain alcohols, such as propanol or isopropanol or other, as a solvent. Solvents, for example propanol, however, are typically volatile. Thus, if a solvent containing lens forming material is dosed into the female mold half of the opened mold, at least a portion of the solvent evaporates before the mold is closed again. Due to the reduced amount of solvent the lens forming material changes its properties, which, after the lens forming material has been polymerized or cross-linked may result in streaks or other defects or undesirable property changes on or in the formed lens. Such defects, such as streaks, if located in the vision area of the lens, may be intolerable so that the lens must be rejected after inspection. In addition, residues of lens forming material having a reduced solvent content may deposit at the tip of the dosing unit and influence the accuracy of the next dosing process in an adverse manner. Also, volatile solvents are very often easily inflammable and/or explosive so that special provisions must be taken if such materials are used.
It is an object of the present invention avoid the evaporation of volatile solvents or to keep the evaporation of volatile solvents, such as, e.g., propanol, from lens forming materials at least at a low level. A method of dosing a lens forming material into a mold is described which allows to obtain ophthalmic lenses, in particular contact lenses, which are free from streaks. In addition, an accurate metering of the lens forming material into the mold shall be possible.